Boron contents of Japan Trench sediments and Iwate basaltic lavas, Northeast Japan arc: estimation of sediment-derived fluid contribution in mantle wedge

Mantle wedge below the Northeast Japan are contains hydrous fluids that deh ydrated from two parts of the descending slab: a sediment layer and an alte red oceanic crust (AOC). In order to estimate the weight percent of a sedim ent-derived fluid in the mantle wedge, we determine boron and other element contents of Japan Trench sediments and Iwate basaltic lavas on the Northea st Japan volcanic front. Trace element contents of the trench sediments are used to estimate those of the sediment-derived fluid, and previously repor ted trace element contents of the AOC are used to estimate those of the AOC -derived fluid. Examination of mobile/immobile element ratios (B/Sm, Ba/Sm, K2O/Sm, B/Zr, Ba/Zr, K2O/Zr) of the two slab-derived fluids and Iwate basa ltic lavas, indicates a mixing ratio between the AOC-derived fluid and the sediment-derived fluid is 90:10 in the mantle wedge beneath the Northeaster n Japan are. The mobile/immobile element ratios also suggest that the subdu cted sediment recycle to the mantle wedge beneath Northeast Japan as sedime nt-fluid rather than sediment-melt. Since the weight fraction of the total slab-derived fluid in the mantle wedge is estimated to be less than 1 wt%, an addition of a small amount ( < 0.1 wt%) of the sediment-derived fluid to the mantle wedge fulfills the boron and other trace element contents in th e Iwate basaltic lavas. <(c)> 2001 Elsevier Science B.V. All rights reserve d.